Swiss Pat. No. 601,567 describes a sports ground covering, with a lower layer for cushioning or damping impact actions on the covering and a thinner wear-resisting coating applied thereto. The lower or cushioning layer stabilized by a reinforcing iron netting, according to a preferred embodiment, contains, apart from rubber chips, which emanate from old vehicle tyres and are bound with polyurethane, mineral additives, enabling the elasticity of the layer to be adjusted to a desired value.
Sports ground coverings constructed in this way have excellent characteristics. However, certain problems occur during their production, as a result of the use of mineral additives. Due to the fact that they consist of chippings, concrete rubble and/or sand, they are hygroscopic. The moisture proportion contained therein consequently varies within certain limits. During the production of the cushioning layer in situ, it is therefore largely a question of how and where the mineral additives were stored beforehand. It is quite possible for the moisture content to change during the production of the sports ground covering, because said contents can be lower during the late afternoon than in the morning when starting work. As a result, the properties of the covering change.
In addition, due to their porosity, said additives also partly absorb the binder, i.e. the polyurethane, namely to an extent which is partly dependent on the particle size of the minerals and therefore makes accurate metering of the binder more difficult. Thus, during manufacture, it is necessary to depend on the values obtained through experience, but this can only gradually be acquired. However, sports ground coverings must have the correct composition from the outset. Furthermore, additional problems are caused by the fact that in the case of excessively high moisture contents of the mineral additives, the polyurethane tends to expand.
Thus, the object of the invention is to replace this additive by a more suitable material, thereby not only simplifying production, but also if possible, carrying out part of the production process beforehand, so that in situ it is only necessary to carry out the actual installation.